motion control

[sidda]

Dear Jochen Klier

When I was trying to increase the acceleration time (Designed in LV) , I have observed the following which I have given below in a tabular form.

Velocity (RPM)      Acceleration (counts/sec2)        DAC count

    100                            100                                    1600

    100                            500                                    3200

As per the calculations concerned to DAC, 100RPM corresponds to 1600counts so 200RPM corresponds to 3200counts and so on.............................

But when velocity is kept constant and when acceleration is increased, In this condition I am getting the DACcount = 3200count.(Obtained when you load 200RPM)

1. Can you pls tell me why DACcount has increased?. 

2. What is the relation between these three parameters?.

Thanking you,

Regards,

S.P.Vani
Jisnu Communications Ltd,

[Brian_Beal]

You need to tell us what hardware you are using.  DAC can mean different things.  If it is a servo system in torque mode, the DAC output has no relation to velocity.

[Jochen]

Sidda,

does this thread belong in any way to the question that you have asked here? As Brian, I'm also a bit confused about the DACcount value that you mention in your post. Please clarify.

Thanks,

Jochen

[sidda]

Dear Mr.Jochen

We have asked two different quieries and they are not related with each other.

The DAC we have mentioned here is related with digital to analog converter(in motion controller) through which we are commanding the drive (we are using an encoder to get the feed back from our system). I hope now understood the "DAC " term used.


Also we didnot receive any suggestion for the query related with usage of PID controller

Do reply at the earliest

Thanks

[sidda]

Dear Mr.Jochen

We have asked two different quieries and they are not related with each other.

The DAC we have mentioned here is related with digital to analog converter(in motion controller) through which we are commanding the drive (we are using an encoder to get the feed back from our system). I hope now understood the "DAC " term used.


Also we didnot receive any suggestion for the query related with usage of PID controller

Do reply at the earliest

Thanks

[Jochen]

Sidda,

I'm sorry but I still don't understand your question exactly. You really need to provide more information about the hardware that you are using (motion controller, drive, drive mode;...). How do you obtain the DAC count values? During a motion profile the output value of a control output is not constant and there is no simple relationship between move parameters and the output voltage in a closed loop system.
During the acceleration phase of course the mean value of the control output will be higher depending on the acceleration value but I'm not sure if this is the piece of information you are looking for.

Please note that I have posted an answer to your other question two weeks ago but you haven't provided the information that I have asked you for.

Best regards,

Jochen Klier
National Instruments Germany

[sidda]

Dear Mr. Jochen,
I will surely send the complete details in my next thread so that you can clearly understand ,analyze and help me out.

Thanking you Sir,

With Regards,
S.P.Vani

[sidda]

Dear Mr.Jochen,

We are developing Antenna Control System (ACS) based on LabVIEW 8.2.platform using NI-7352 motion controller card, NI-6229 digital card and UMI 7774 opto-isolator interface card. The ACS is required to drive a Servo mechanism comprising of a servo motor SEM make (Rated speed of 6000 rpm) with a suitable servo power amplifier.

We have two different systems to be rotated at different speeds. One system is to be rotated at the rate of 1800 rpm and the other at 4000 rpm. These are the max velocities at which these systems are to be rotated. For a discussion on the problems we are facing we shall take the case where the max velocity at which the system is to be rotated is1800 rpm. Please find the following observations.

1. The system is on position loop feedback using a combination of absolute and incremental encoders. The velocity parameter is calculated based on the encoders feedback

2. The PID set parameters are

Case 1. kp=12, kd= 0, kv=0

            When these values are loaded my system does not go more than 900rpm.

Case 2.  kp=25, kd= 50, kv=0,Td=0

For these values my system does not go more than 1300rpm. Also I could observe jerky movements physically on the antenna movement.

Case 3. kp=30, kd= 60, kv=0, Td=0

At this point the system could go up to 1700rpm also. But the jerky movements have increased substantially.

Also the system comes to a halt if the velocity is set more than above values in each case after the max velocity in each case.

      3.   The antenna was driven by directly connecting the motor and power amplifier to it and   observed the system rotating smoothly and to the rated speed without any jerks, which does rules out ant problems with the motor, power amplifier or the mechanical system.

We have the following to be addressed.

1. We want the system to be run to the max velocity rating of the motor, which we are unable to carryout.
2. At the different speeds at which we are working we need the ACS to drive the antenna on a smooth curve without any jerks.

Please suggest ways to achieve the above. Please let us know the PID settings are correct or what modifications we need to carry out. At present we are setting these values based on our experience and we do not possess PID tool kit.

We have done quite a number of tests in tuning the motor and have an idea of what happens when kp or kd or ki is changed to some extent.

Look forward for your early response.

Vani, Engineer, Jisnu Communications Ltd.

[T-Route]

Hello sidda,

It is hard for us to determine whether or not the PID settings you have listed are correct.  It depends on the torque and load the motor is working with that will make these values optimum.  If you are experiencing jerky movements and you are unsure of how to set the PID gains manually then I would suggest trying the "Auto Tune" functionality in Measurement and Automation Explorer.  I have included a very good link below that will explain how to tune your servo motor in Measurement and Automation Explorer and explains what all the settings mean.  I hope this information helps.  Thanks and have a great day.

Understanding Servo Tune

Regards,
Mark T
Applications Engineer
National Instruments